A speaker of the related art will be described below with reference to FIG. 14. FIG. 14 is a cross-sectional view of a speaker of the related art.
As shown in FIG. 14, speaker 110 includes speaker diaphragm 101 (hereinafter referred to as diaphragm 101), magnetic circuit 105, speaker frame 107 (hereinafter referred to as frame 107), and voice coil 108. Magnetic circuit 105 is configured by sandwiching polarized magnet 102 between upper plate 103 and yoke 104. Frame 107 is coupled to yoke 104. An outer periphery of diaphragm 101 is coupled to an outer peripheral portion of frame 107 by way of edge 109. One end of voice coil 108 is coupled to a central portion of diaphragm 101. The other end of voice coil 108 is arranged to fit into magnetic gap 106 formed by magnetic circuit 105. Speaker dust cap 111 (hereinafter referred to as cap 111) is coupled to a front surface portion of diaphragm 101. Voice coil 108 includes tubular voice coil body 108a, and has a structure in which coil 108b is wounded around an outer peripheral portion of voice coil body 108a. An inner periphery of damper 112 is coupled to voice coil 108, and an outer periphery of damper 112 is coupled to frame 107. Speaker 110 is configured in such manner.
Diaphragm 101 is made of resin such as polypropylene (hereinafter referred to as PP), and is formed by injection molding a thermally fused resin pellet into a molding die set with a shape of diaphragm 101. A single material such as PP is generally used for the type of a resin material used in injection molding.
Blend-type diaphragm 101 using different types of resin also exists for the purpose of adjusting characteristic value for diaphragm 101, that is, adjusting characteristics or sound quality for speaker 110. Furthermore, in adjusting the characteristic value where adjustment is difficult only with a resin, adjustment of the characteristic value of diaphragm 101 and adjustment of the characteristics for speaker 110 or sound quality are carried out by mixing a reinforcing material such as mica. Moreover, in order to increase a degree of freedom in adjusting the characteristic value, the sound quality adjustment of diaphragm 101 is carried out by mixing a pulp material. Such speaker 110 of the related art is disclosed in, for example, patent document 1 and patent document 2.
The single material such as PP is also generally used for cap 111 used in speaker 110, similar to diaphragm 101. Speaker 110 of the related art using cap 111 is disclosed in, for example, patent document 3.
Such diaphragm 101 of the related art uses a manufacturing method by papermaking, or a manufacturing method by injection molding or pressing of a resin. Thus, diaphragm 101 of the related art is made of paper or is made of a resin.
Therefore, diaphragm 101 uses different materials depending on the application while exploiting the features of each material. However, each has problems, and it is difficult to satisfy the market demand such as lower distortion, wider band, and higher dynamic range. Furthermore, in the production of diaphragm 101 made of paper, lowering the cost of the component is difficult as great number of steps of papermaking is required. In diaphragm 101 made of a resin, on the other hand, only the standardized characteristic value specific to the resin or the material can be obtained. Thus, the adjustment range of the characteristics and the sound quality for speaker 110 is very narrow.
Diaphragm 101 in which the resin and the pulp material are mixed has a large degree of freedom in the sound quality adjustment, and moisture resistance reliability is also improved. However, diaphragm 101 of the related art has a problem in that the strength is insufficient to enhance the sound quality.
Cap 111 used in speaker 110 also is made of the material and the manufacturing method of cap 111 is similar to diaphragm 101. Therefore, cap 111 has the same problems as diaphragm 101 of the related art.
Frame 107 is desired to have high rigidity, a damping effect, and high internal loss so that the vibration of diaphragm 101 does not transmit to magnetic circuit 105 or resonance is less likely to occur. Frame 107 of the related art thus mainly is made of an iron plate, a material of an aluminum die-cast, or a resin.
However, frame 107 made of the iron plate has problems in that magnetic leakage is large, and the external appearance also lacks in sophisticated image. Frame 107 made of the material of aluminum die-cast excels in magnetic leakage and external appearance quality, and has high rigidity. However, frame 107 made of the material of aluminum die-cast has a problem in that it is very expensive. In order to solve such problems, a thermoplastic synthetic resin is often being injection molded to be molded to the shape of frame 107 and used in recent years. In particular, frame 107 made of the resin has a large degree of freedom in a shape, and is suited for a lighter weight. Speaker 110 using such frame 107 is disclosed in, for example, patent document 4.
However, such frame 107 made of the resin of the related art may be light weight, but does not have enough rigidity with only the resin of a base material. Thus, an inorganic filler such as a glass fiber or mica is often added. In particular, from the aspects of lighter weight, moldability, acoustic performance, and the like, PP having a small specific gravity and large internal loss is used for the resin of frame 107. The addition of the inorganic filler of greater than or equal to 30% by weight is required to satisfy the acoustic performance of frame 107. The rigidity of frame 107 becomes higher by adding the inorganic filler. However, the specific gravity of frame 107 also increases, and thus the weight of frame 107 becomes heavy. Moreover, a problem in that the effect of absorbing unnecessary vibration reduces arises since the internal loss of frame 107 becomes small.
A method for manufacturing diaphragm 101 of the related art will now be described with reference to FIG. 15. FIG. 15 is a process chart showing the method of manufacturing speaker diaphragm 101 made of a resin using injection molding of the related art.
As shown in FIG. 15, resin 114 such as PP is dry blended with PP 115 with a reinforcing material such as mica to produce master batch 116. Master batch 116 is then pelletized to produce master batch pellet 117 (hereinafter referred to as pellet 117). Pellet 117 is then injected in an injection molding machine to thereby manufacturing a speaker component such as diaphragm 101.
In the injection molding machine, injected pellet 117 is heated and melted through a heating step. It is then injected into molding die 118 for diaphragm 101 using an extruder. The injected PP resin is cooled and solidified, and then taken out from the molding die 108, thereby forming diaphragm 101. Diaphragm 101 made of a resin typified by PP and the like is manufactured using such an injection molding step.
A single material such as PP is generally used for the type of resin material used in injection molding. In addition to the PP, blend-type diaphragm 101 in which different types of resins are mixed also exists for the purpose of adjusting a characteristic value for diaphragm 101, that is, adjusting characteristics and sound quality for speaker 110.
A method for manufacturing blend-type diaphragm 101 includes grinding a plurality of types of resin pellets to be mixed using a grinder, where a blending ratio is set. Mixing is performed by dry blending, which is then used to manufacture diaphragm 101.
Such a method for manufacturing speaker 110 of related art is disclosed in, for example, patent document 5.
In order to respond to the market demand on the speaker component such as diaphragm 101, in particular, from the standpoints of quality stabilization and water resistance reliability, and furthermore, diversification of design, diaphragm 101 made of a resin is very popular.
However, in the method for manufacturing the speaker component such as diaphragm 101 of the related art, diaphragm 101 made of a resin has a problem in that adjustment of the characteristics and the sound quality for speaker 110 can only be carried out within a range of the characteristic value of the material of the resin being used, and only a standardized sound can be generated.    [Patent document 1] Unexamined Japanese Patent Publication No. S59-176995    [Patent document 2] Unexamined Japanese Patent Publication No. 2005-236497    [Patent document 3] Unexamined Japanese Patent Publication No. H03-289298    [Patent document 4] Unexamined Japanese Patent Publication No. 2003-37891    [Patent document 5] Unexamined Japanese Patent Publication No. H01-248900